With the multitude of scanning, transmission and display formats, it becomes increasingly likely that material generated for a targeted application display will end up being shown on other display devices with differing capabilities. This may be the case for spatial resolution, amplitude resolution, color resolution, frame rate, scanning format, etc. Alternatively, a given display device may end up having to show materials which differ in these aspects. Streaming video applications is one example where this might occur. Historically, interlaced and progressively scanned material has been targeted for different applications. However, video streaming applications have led to cases where both interlaced and progressive material are shown using only one display scan format. Video streamed to a progressively scanned PC display may consist of a combination of television and film content, or interlaced and progressive material.
How to best display interlaced material on progressive scan displays or vice-versa is a difficult problem and has been the subject of many de-interlacing, subsampling, interpolation, and frame-rate change, etc. studies. What further complicates the problem in the streaming video case is the fact that it is often not known whether the streamed material is progressive or interlaced to begin with. During a movie segment the material may be progressive scan, but during commercials the content may switch to interlaced format.
Because the streamed video data may not always convey the correct scanning information (if at all), it may be useful to be able to deduce the scanning format from the raw video itself. Due to the existence of (bad) edits in the material, the fact that interlaced material is often assembled into frames using two consecutive fields, etc. makes a method for automatically determining scan format useful. Moreover, even film material which has undergone field pulldown will have a mixture of both progressive and interlaced-like content.
In addition, for display, compression, or processing of interlaced material, it is important that correct timing of fields be maintained. If the top and bottom fields of interlaced material are not displayed in the proper order, severe visual artifacts can occur especially for high motion scenes. Displaying fields in reverse order results in data not being shown in chronological order. If compression or processing of interlaced material uses temporal motion models, then maintaining correct chronological order of fields is important. Otherwise, compression efficiency or video quality may be sacrificed.
In many traditional video applications, the proper field order can be obtained from some temporal side information stored or transmitted with the interlaced video. However, in today's emerging and converging world of television and Internet streaming video, it becomes increasingly possible that information about field order is lost or not known. Interlaced video may be processed for both interlaced and progressive display, and it may undergo some editing operations which may alter the display order of the fields. In some cases, only the raw interlaced video data may be known and information about the field order may not be given.
The present invention is therefore directed to the problem of developing a method and apparatus for automatically detecting the correct field order from only the interlaced video data, without any side information knowledge except for the spatial resolution, as well as for differentiating between progressive and interlaced material using the video content itself.